The present application relates to an ionic compound, an electrolytic solution using it, an electrochemical device using it, and a battery using it.
An ionic compound has been widely used in various fields. As an example, in the electrochemical device field, an ionic compound containing an anion such as PF6− and BF4− has been used as an electrolyte salt making much account of the solubility, the ion dissociation property and the like.
Of the electrochemical devices, in the field of the battery mainly used as a power source of electronic devices, particularly in the field of the secondary battery capable of being charged and discharged, research and development to improve the battery characteristics such as the capacity characteristics and the cycle characteristics are actively made. Specially, a secondary battery using insertion and extraction of lithium ions for charge and discharge reaction (so-called lithium ion secondary battery) or a secondary battery using precipitation and dissolution of lithium ions (so-called lithium metal secondary battery) is extremely prospective, since such a lithium ion secondary battery or such a lithium metal secondary battery can provide a higher energy density compared to the existing lead battery and the existing nickel cadmium battery.
In such a secondary battery, an electrolytic solution in which an electrolyte salt such as LiPF6 is dissolved in an ester carbonate-based nonaqueous solvent such as propylene carbonate and a diethyl carbonate is widely used making much account of the electric conductivity, the electric potential stability and the like. As the electrolyte salt, LiBF4, LiCF3SO3, LiClO4, LiAsF6, LiN(CF3SO2)2, LiN(C2F5SO2)2, LiN(C4F9SO2)(CF3SO2) or the like is used in addition to LiPF6. Further, in recent years, bis(oxalate)lithium borate, bis(salicylate)lithium borate, bis(malonate)lithium borate, (malonate oxalate)lithium borate, bis(succinate)lithium borate, (difluoro oxalate)lithium borate, (tetrafluoro oxalate)lithium borate or the like is used (for example, refer to Japanese Unexamined Patent Application Publication Nos. 07-065843, 2003-536229, 2004-534735, 2005-079057, and 2005-005114). It is proposed that bis(malonate)lithium borate, (malonate oxalate)lithium borate, or bis(succinate)lithium borate is used to improve the heat resistance and the like in the electrochemical device field.
However, the existing ionic compound is not sufficient yet in terms of the solubility and the chemical stability. Therefore, in the electrolytic solution and the electrochemical device using the existing ionic compound, the performances are limited accordingly. More specifically, sufficient chemical stability is not able to be obtained in the electrolytic solution, and sufficient cycle characteristics are not able to be obtained in the secondary battery.